The election marks the first democratic transition of power in the nuclear-armed state but the run-up to the polls has been marred by attacks that have killed at least 130 people since mid-April, according to an agency toll.

"We proudly claim responsibility for this attack, we carried it out and will carry out more of the same," Ehsan said of the first deadly attack on polling day.

More than 600,000 security personnel are being deployed nationwide and around half the estimated 70,000 polling stations have been declared at risk of attack, many of them in insurgency-torn parts of Baluchistan province and the northwest.